1. Field of the Invention
The present invention relates to a base station of a code division multiple access (CDMA) digital cellular communication system and, in particular, to apparatus and methods for tracking a power level of a received signal.
2. Description of the Related Art
Generally, in an analog cellular communication system, transmitting power sent from a mobile telephone subscriber is controlled by measuring a power level of a signal received at the base station of such system. If the power level of the signal received at the base station from a mobile telephone is less than a reference value, the system will increase the transmitting power of the mobile telephone. On the other hand, if such power level is greater than the reference value, the system will decrease the transmitting power of the mobile telephone. In a conventional analog cellular communication system, the power level of the signal received at the base station is measured by using a level of a received signal strength indicator (RSSI).
Similar to the analog cellular communication system, a CDMA communication system (which is a recent digital cellular communication system) requires an operation for controlling the transmitting and receiving powers in order to maintain a maximum traffic capacity. The CDMA communication system differs from the conventional analog cellular communication system, however, in that the base station of the CDMA communication system includes a variable attenuator within a receiving frequency conversion board of a transceiver unit in a backward link in order to accurately control the transmitting and receiving powers. Specifically, an RSSI value of the received signal varies according to a control voltage of such variable attenuator. Therefore, if the control operation used in the base station of the conventional analog cellular system is utilized in the CDMA communication system, it is difficult to accurately track the power level of the received signal (which is a representative parameter in the operation for controlling the transmitting and receiving powers) without using an additional algorithm to consider an attenuation of the variable attenuator.